Cotton Yield Is Affected by the Distribution of Chlorophyll Content Response to Sowing Date and Planting Density
Chlorophyll content,which is related to nitrogen metabolism,is a commonly used diagnostic index of supplied nitrogen nutrition conditions in the field.[Objective] In this study,we examined the effect of sowing date and planting density oncotton nitrogen metabolism under late and direct seeding conditions.[Method] A split-field design,with sowing date (S1,May 30;S2,June 14) as the main plot and density (plants·m-2) (D1,7.5;D2,9.0;D3,10.5) as the subplot,was used to measure the dynamics of chlorophyll contentamong nitrogen metabolism that was discussed in this paper.[Result] We found that cotton chlorophyll a,b and (a+b) contents were highest at peak bloom,followed by first bloom and then squaring;the contents of leaves,which increased moving downwards from the top of the plant to the 3rd to 5~ leaves and then dropped,decreased with increased planting density.Except for chlorophyll b during squaring,planting date S2 resulted in higher chlorophyll contents during squaring,first bloom and peak bloom than S 1;however,differences among leaf positions were not altered by either sowing date or density.Cotton chlorophyll a/b values were highest at squaring,followed by first bloom (peak bloom).In regard to leaf position,this ratio increased moving downwards from the top of the plant to the 3rd to 4th leaves;values then decreased at squaring but only changed gradually at both first bloom and peak bloom.Neither sowing date nor density had an effect on differences among leaf positions.We used stepwise regression analysis to choose an individual leaf position with a chlorophyll content corresponding to the average for the entire plant.The typical cotton leaf representing chlorophyll status was identified as the 5th leaf during squaring and the 4th leaf during first bloom,but varied during peak bloom.[Conclusion] In short,S 1 D2 gave the highest yield with the optimum chlorophyll (a+b) content and chlorophyll a/o value.
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